To optimize the content determination method of morphine sulfate suppositories, which had high toxicity of extraction solvent and poor specificity and generality of chromatographic conditions.

The optimization of the preparation method for the test solution was to prepare the test solution by ice bath freezing and n-heptane extraction, and to compare the content determination results of the test solution prepared by the United States Pharmacopeia method (extracted with trichloromethane). The optimization of chromatographic conditions for content determination was based on the comprehensive comparison of United States Pharmacopeia, British Pharmacopeia and YBH specification. Symmetry C₁₈ column (150 mm×4.6 mm, 5 μm) was finally used. The mobile phase was 0.01 mol·L^-1 potassium dihydrogen phosphate solution containing 0.202% sodium heptane sulfonate (containing 0.1% triethylamine, adjusted to pH 2.5 with phosphoric acid) -methanol (70∶30). The flow rate was 1.0 mL·min^-1. The column temperature was 30 ℃. The detection wavelength was 284 nm. The injection volume was 20 μL.

The content measured by ice bath freezing method was relatively low, while the content measured by n-heptane extraction and trichloromethane extraction was basically consistent, indicating that n-heptane could be used as extraction solvent instead of halogenated alkane. The linear range of morphine sulfate was 2.12-105.94 μg·mL^-1(r=0.999 9), and the LOQ was 10.60 ng. The RSD values of system precision, repeatability, intermediate precision and stability were all less than 2%. The average recoveries were 98.6%-99.6% and RSD was 0.21%-0.66%. After forced degradation, the main peak of the tested solution could be separated from the degraded impurities, with good specificity. By changing the flow rate, column temperature, pH value, mobile phase ratio and column brand, the main peak could be well separated from each impurity peak, with good robustness.

This study optimized the determination method for morphine sulfate suppositories. The preparation of the test solution used n-heptane instead of the highly toxic haloalkane, and meanwhile improved the chromatographic conditions, enhanced the environmental protection, specificity and applicability of the method. It can be used for the content determination of morphine sulfate suppositories.